Metal enolates thermochemical considerations

Examples of thermochemical considerations of cupric enolates include the study of the binding of Cu + with kojic acid (16), a cyclic a-ketoenol. Comparison was made between the divalent cations of U02 +, Cu +, Zn +, Ni +, Co +, Cd +, Ca + where these metals are listed in decreasing order of binding constants over 6 powers of 10. In this case carbon-bonded metal seems most unreasonable because it would ruin the chelation as well as any aromaticity in the pyrone ring. It is admittedly an assumption that pyrones are aromatic. There are no one-ring pyrones for which there are enthalpy of formation data for gas phase species, as opposed to the benzoannelated compounds coumarin (I7)i07a, I07b chromone (is) " " "and xanthone (19) . Plausible, but unstable, Cu(II) enolates eliminate copper and form the 1,4-dicarbonyl compounds as shown in equation 8. 

---